1. Field of the Invention
The present invention relates to a compression system, a program and a method for compressing a motion picture. More particularly, the present invention relates to a compression system, a program and a method for compressing a motion picture generated by projecting objects in a three-dimensional (3D) space onto a screen.
2. Description of the Related Art
In a software application for displaying a virtual world such as the 3D Internet and online games, the process of rendering objects from a 3D space onto a two-dimensional (2D) screen is performed by a client. However, when the client does not have sufficient processing capabilities, a server, instead of the client, renders the objects from the 3D space onto the 2D screen. Moreover, the server transmits a result of rendering to the client after compressing the result by use of a motion picture compression method such as MPEG (Moving Picture Experts Group).
In the motion picture compression method such as MPEG, a difference image between an uncompressed image and a predicted image predicted from a reference image by motion compensation is calculated for a frame to be compressed, referred to as a compression target frame. This difference image is image-compressed by DCT (discrete cosine transform) or the like. Such motion picture compression method enables efficient compression using motion compensation based on a motion vector.
When accurate motion compensation is performed, the difference image is reduced in size. When the difference image is small, a size of compressed data is also reduced. Therefore, in the case where a motion picture is compressed by motion compensation based on the motion vector, detection of an accurate motion vector is important for enhancing compression efficiency. However, a computational effort for detecting the motion vector takes up a large part of motion picture compression processing. Accordingly, when the computational effort required for motion vector detection processing is increased in order to enhance the compression efficiency, the entire processing speed for the compression processing is slowed down and, as a result, the processing cost is also increased.